Run a stepper from 2 DM542 drive

[BeagleBrainz]

I wouldn't assume -DIR or -STEP are connected to ground, the output circuit could be a NPN transistor (open collector). So the safest bet would be to put each (for lack of better description signal) on a separate pole.
Maybe the output circuit of one of the boards can recognize an open circuit, on either the STEP or DIR causing a fault condition.
The user has provided no circuit diagrams so it is really hard to say which way to jump.

It would be the same as asking a programmer to design a routine to process a data packet without actually telling them anything about the format of the data packet.

[A_Camera]

The user has provided no circuit diagrams so it is really hard to say which way to jump.

Yes, that's the key issue. We are all only guessing. I provided my solution, but yes, other solutions might be needed, we have no idea since we don't have enough information about his design. I was however very clear that the solution I proposed is what I use and it works for me, and I bet you that I could make it work with his driver also.

There are two documented possible ways of connecting the driver, in one case you bridge all the + to the same and switch all the - signals, the other way is what I am using, which is I think the most commonly used. Basically there is very little difference between them (I know that electrically the difference is huge), and both uses the same principle, but without knowing all the details of his solution it is impossible the say which is right and which is wrong.

[A_Camera]

The user has provided no circuit diagrams so it is really hard to say which way to jump.

Yes, that's the key issue. We are all only guessing. I provided my solution, but yes, other solutions might be needed, we have no idea since we don't have enough information about his design. I was however very clear that the solution I proposed is what I use and it works for me, and I bet you that I could make it work with his driver also.

There are two documented possible ways of connecting the driver, in one case you bridge all the + to the same and switch all the - signals, the other way is what I am using, which is I think the most commonly used. Basically there is very little difference between them (I know that electrically the difference is huge), and both uses the same principle, but without knowing all the details of his solution it is impossible the say which is right and which is wrong.